PLASMA DARK CURRENT IN SELF-IONIZED PLASMA WAKE FIELD ACCELERATORS∗

Evidence of particle trapping has been observed in a beam driven Plasma Wake Field Accelerator (PWFA) ex-periment, E164X, conducted at the Stanford Linear Ac-celerator Center by a collaboration which includes USC, UCLA and SLAC. Such trapping produces plasma dark current when the wakefield amplitude is above a thresh-old value and may place a limit on the maximum acceler-ation gradient in a PWFA. Trapping and dark current are enhanced when in an ionizing plasma, that is self-ionized by the beam. Here we present experimental results